Accurion GmbH // Stresemannstraße 30 // 37079 Goettingen

Δ and Ψ, have been measured with a nulling Imaging Spectroscopic 
Ellipsometer EP³ SE, equipped with 2x, 10x objectives, and automatic sample 
alignment stage. The measurements were carried out within the wavelength 
range 360-1000 nm at 70° angle of light incidence. The data were acquired and 
evaluated by EP3View Software. Inhomogeneity of the film thickness and 
optical properties was studied in three steps. As the first step, Δ and Ψ spectra 
of 10 regions of interest (ROIs) were acquired simultaneously in the high 
plasma flow area (edge of the wafer) and spectrum of one ROI in the low 
plasma flow area (centre of the sample). Each ROI was corresponding with 0.3 
mm x 0.3 mm sample surface area, over which Δ and Ψ was averaged. Notice, 
that ROI-
size and lateral resolution (here 4 μm) can be much smaller than 
beam size (here 2 mm diameter) in imaging ellipsometry. The spectra were 
averaged over four measuring zones. Spectra of one ROI in the high plasma 
flow area are given in Fig. 1. The ellipsometric data were fitted to a 4-layer 
model including air, ITO film, SiO2 film and Si substrate, providing thickness of 
the films. The model does not include surface roughness because AFM 
measurements show root-mean square roughness of the film below 1 nm that 
is less than the accuracy of the film thickness determination. 
References: 
Vaupel M., Vinnichenko M. (2008) Plasma flow induced local variation of dispersion constants of ITO-
films observed with spectroscopic imaging ellipsometry. physica status solidi 5, 1137
–1140 
 
Optical modeling: 
A frequently used way to parameterized the optical properties of an ITO-layer is 
a Drude-Lorentz approach. Depending on the substrate surface and ITO 
surface, respectively, a roughness layer or a mix interlayer is required for a 
proper modeling. 
CONCLUSION 
Imaging ellipsometry is the method of choice for thin film methrology of 
patterned self assembled thiol monolayers on gold surfaces. The technique has 
been used for pattern with changing packing density, with different chemical 
endgroups, changing chainlength and substrate selective patterning. In the 
most cases the authors have used a single wave imaging ellipsometer, 
performing maps and angle of incident spectra. 
a) 
b) 
c) 
d) 
Figure 2. Local-scale maps of ITO film thickness, 
Lorentz oscillator force, free electron density, and 
mean square error (MSE).